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Abstract A spinel ferrite sample Zn 0.4 Ni 0.6 Fe 2 O 4 was prepared by a conventional solid-state reaction method at high temperature. This compound was found to exhibit a single phase and crystallize in a cubic structure with Pm3 m Space group. The complex impedance was investigated in the temperature range 400–700 K and in the frequency range 100 Hz - 1 MHz. The Z-impedance analysis revealed that the relaxation phenomenon is strongly dependent on temperature and frequency. The impedance plane plot showed semi-circle arcs at different temperatures, and a proposed electrical equivalent circuit explained its results. The temperature and frequency dependence of the ac conductivity was shown to obey the universal Jonscher's power law. The activation energy, inferred from the impedance spectrum, was confirmed to match very well with those estimated from the conduction mechanism, indicating that the relaxation process and conductivity have the same origin. The magnetization is due to the ferromagnetic interactions between iron ions. Graphical abstract Highlights • The complex impedance plots have revealed the presence of three semicircular arcs. • Values of the activation energy calculated from σ ac and Z″ are very close. • The electrical properties are strongly dependent on both temperature and frequency. • The applied field frequency enhances the electronic jumps between the localized states. • The ferromagnetic contribution presents 70% of the total magnetization. [ABSTRACT FROM AUTHOR]